A battery pack has been already used in various portable apparatuses such as a mobile phone, a digital still camera, a portable game machine, a notebook personal computer, and an electric tool. Currently, the battery pack is used not only in these apparatuses, but in a field, in which a higher output and higher capacity are required, such as an electric power-assisted bicycle, an electric vehicle, and further a home-use power storage device.
As a secondary battery cell built in the battery pack, one of the secondary battery cells mainly used currently is a lithium-ion secondary battery cell. The lithium-ion secondary battery cell is used in a very wide range because of its considerable characteristics, i.e., it can be repeatedly used by being charged; it outputs with a high voltage; it has a high energy density; the self-discharge is small; and it has a long life. To respond to the request for the apparatus to have a higher output and a higher capacity, there are increasing cases where the secondary battery cells (single cells) are connected in multi-series or in multi-parallel and used in a form of an assembled battery. There are many advantages in using the secondary battery cell in this way. However, the secondary battery cell has to be more carefully used than ever before, since the used energy amount becomes very large by using it in this way.
Generally, the battery pack is monitored regarding its state, such as an overcharge, an over discharge, an overcurrent, and a temperature. The battery pack includes a control circuit having a battery protection circuit so as not to be used in a dangerous state or a state where the characteristic degradation is caused. Traditionally, when the battery protection circuit operates, the charge/discharge operation of the battery pack as a whole is appropriately stopped so as to guarantee the safety of the battery pack or the electric power consumption device, in which the battery pack is built. Generally, the temperature state of the entire battery pack is monitored. Monitoring the overcharge, the over discharge, and the overcurrent is performed in regard to each secondary battery cell. However, it is actually performed based on the complicated process, in which a measuring unit for measuring a current flowing in each secondary battery cell and a terminal voltage of the secondary battery cell is provided in each secondary battery cell, and the control circuit provided in the battery pack receives the value obtained by the measuring unit through wire transmission, and the control circuit obtains a current value and a terminal voltage value.
A battery authentication system authenticates the secondary battery cell provided in the battery pack to determine whether the battery pack mounted in the electric power consumption device can be safely used for the electric power consumption device. The battery authentication system is widely used, and a technique for reading individual identification information, such as an ID number, from the secondary battery cell including a wireless IC tag is well known from, for example, Japanese Patent Application Laid-Open No. 2006-236806.